Enhancement of electromagnetic barrier properties

ABSTRACT

A method and structure for enhancing electromagnetic barrier properties including a substrate, a coating deposited upon the substrate, and a plurality of sets of patterns microembossed upon the surface of the coating layer for increasing the barrier properties of the structure. The plurality of sets of microembossed patterns each having a line density between about 100 and 50,000 lines per square centimeter.

This is a continuation of application Ser. No. 07/973,842, filed on Nov.9, 1992, now U.S. Pat. No. 5,310,576, which is a continuation of U.S.patent application Ser. No. 07/471,415, filed on Jan. 29, 1990, now U.S.Pat. No. 5,211,997.

This invention relates to cellular materials, including cellulosicmaterials, and more particularly the enhancement of such electromagneticbarrier properties as optical density and thermal insulative effect.

Cellular materials have a desirable thermal insulative property byvirtue of the presence of cellules of air interspersed among the fibersthat constitute the overall structure of the materials.

However, because of the air nodules, there is a degree of light porositythat is undesirable in many cases.

Accordingly, it is an object of the invention to increase theelectromagnetic barrier properties of materials. Another object of theinvention is to reduce the light porosity of cellulosic and othermaterials consitituted by structures having a high degree of porosity.

Another object of the invention is to increase the thermal insulativeeffect of such materials.

SUMMARY OF THE INVENTION

In accomplishing the foregoing and related objects the inventionprovides a method of altering the properties of a structure by providinga substrate, applying a surface layer upon the substrate, and modifyingthe surface layer to increase the barrier properties of the structure.

In accordance with one aspect of the invention the modifying step can beaccomplished by increasing the surface reflectance of the surface layer.

In accordance with another aspect of the invention the modifying stepentails the step of forming a succession of elevations and depressionsin the surface layer upon the substrate. In particular, the modifyingstep can be achieved by forming angled peak and valleys in the surfaceof the layer for increasing the barrier properties of the structure.

A structure in accordance with the invention includes a substrate, alayer upon the substrate, and means upon the surface of the layer forincreasing the barrier properties of the structure.

In accordance with one aspect of the structure, the layer is metallicand bears an embossed pattern. A particularly desirable form of thesurface pattern is microembossed. The microembossed pattern desirablyhas a line density between about 1,000 and 50,000 lines per centimeter.However, a suitable line density can be in the range from about 100 to1,000 lines per square centimeter.

In accordance with a further structure for exhibiting enhanced barrierproperties, a coating is deposited upon a substrate, and a specialpattern is formed in the coating so that barrier properties of thestructure are increased. The coating can be a metallic layer having athickness less than one millionth of an inch, or about 0.4 millionths ofa centimeter (400 angstroms).

In accordance with a further structure for exhibiting enhanced barrierproperties, the substrate is cellular and can be of expanded foam. Thecoating can be formed by vaporization and condensation upon a substrate.

In a further method of enhancing the barrier properties of a substrate,a surface coating is applied to a substrate and the surface of thecoating is modified in order to increase the degree of reflectance ofincident electromagnetic energy of falling upon the coating. Thisreduces the penetration of the substrate by incident electromagneticenergy. The electromagnetic energy can be in the range of visible light.Alternatively, the incident electromagnetic energy can have a frequencybelow infrared, or be in the range of ultraviolet and beyond. Thecoating can be formed by vaporization and condensation, for example byvacuum metallization.

The metallized coating can be provided with an irregular surfacepattern, for example in at least two different degrees of variation. Thepatterns can be in the form of surface corrugations which are disposedat an angle with respect to each other, The patterns advantageously format least a right angle between them, The surface irregularities can beprovided by at least three different patterns. The surface patterns canbe uniformly distributed to form a symmetric repetitive pattern on thesurface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspect of the invention will become apparent after consideringseveral illustrative embodiments taken in conjunction with the drawingsin which:

FIG. 1A and 1B are samples of a material with enhanced barrierproperties in accordance with the invention;

FIG. 2 is a diagram illustrating one possible explanation for theenhanced barrier properties achieved in accordance with the invention;

FIG. 3 is a diagram illustrating another possible explanation for theenhanced barrier properties achieved in accordance with the invention;

FIG. 4 is a further sample of a material with enhanced barrierproperties in accordance with the invention;

FIG. 5 is yet another sample of a material with enhanced barrierproperties in accordance with the invention;

FIGS. 6 and 7 are further samples of a material with enhanced barrierproperties in accordance with the invention.

DETAILED DESCRIPTION

With reference to the drawings, FIG. 1A shows a sample of material 10with enhanced barrier properties in accordance with the invention. Alsoshown in FIG. 1B is an illustrative cross-section of the sample.

The material 10 is formed by a substrate 11, which in the case of FIG.1B is of cellulosic material. It will be understood that the substratemay be of any suitable material including various plastic films ofpolyethylene, polypropylene and the like. Superimposed upon thesubstrate 11 is a coating 12, which in the case of FIG. 1B is a thinmetallic film of the kind produced by vacuum metallization in which ametallic substance,-such as aluminum, is vaporized and then condensedupon the substrate 11.

The invention achieves a suitable barrier to electromagnetic radiation,ranging from ordinary electromagnetic radiation associated with radioand microwave transmissions, through the frequencies associated withheat energy, including infrared radiation, and extending through thevisible spectrum to ultraviolet radiation and beyond. This isaccomplished by special treatment of the coating 12. In particular, thecoating 12 is provided with a prescribed set of surface modifications,such as those achieved by particular indentations 13. These function invarious ways described below to achieve a barrier effect. Theindentations 13 are applied to the surface in a preassigned pattern. Inthe case of FIG. 1A the patterns are in a plurality of sets such thatone set of reflects incident energy having a first angle of incidenceand another set reflects energy having a another angle of incidence,different from the first. In addition, the various patterns are repeatedand provided with a specified degree of symmetry.

One possible explanation for the enhanced barrier properties achieved bythe invention is illustrated in FIG. 2 which shows sinusoidal surfaceirregularities produced by the invention so that incident energyrepresented by the ray R falls upon a bulge as shown and is partiallyreflected as indicated by the ray R'. Because of multiple reflectionsfrom the bulges and their redirection into adjoining regions of thecoating, it is speculated that they produce components which havevarious phase relations with one another and produce a high degree oncancellation of the transmitted components.

Another possible explanation for the enhanced barrier propertiesachieved by the invention is illustrated in FIG. 3 where the surfacecoating of the substrate has been provided with a set of irregularitiesso that the incident energy that falls upon the irregular pattern has topenetrate additional material in the regions where the coating has beenagglomerated as compared with the adjoining regions where the amount ofcoating has been reduced. The overall effect of the change in thedistribution of mass of the coating is believed to enhance the barrierproperty.

More over, because the surface coating has been provided with a seriesof hills and valleys, the reflective surface of the coating isincreased. This also contributes to the improved barrier effect. Theedge of the substrate where the coating has been applied without theirregularities that characterize the invention, shows a ray that strikesat an angle of incidence and is partially reflected. However, since theamount of mass through which the penetrating energy passes isconsiderably less than for those regions where there is an irregularsurface pattern, there is a reduced barrier effect.

In tests that have been conducted of a surface pattern which has beenirregularized in accordance with the invention, as compared with smoothedge strips of the coating where no irregularity has been produced, thebarrier effect of the invention has been significantly demonstrated.

In addition, the barrier properties of the invention are enhanced byforming various irregular patterns which further tend to producemultiple reflections of the incident energy and further produce massagglomerations that attenuate the energy that does manage to penetratethe coating.

Examples of various patterns that provide an enhanced barrier effect areshown in FIGS. 4-7. In some cases the patterns are symmetric, in othercases they are antisymmetric, in all cases there are various patternswhich are distributed across the surface of the substrate for whichenhanced barrier properties are desired.

We claim:
 1. A method of altering the electromagnetic barrier propertiesof a structure which comprises the steps of:(a) providing a substrate,(b) applying a surface layer upon said substrate, and (c) modifying saidsurface layer by microembossing said surface layer with a plurality ofsets of patterns, said plurality of sets of microembossed patterns eachhaving a line density between about 100 and 50,000 lines per squarecentimeter and having a depth less than the thickness of said surfacelayer such that said substrate is not altered, in order to increase thebarrier properties of said structure, said surface layer beingmetallized.
 2. The method of claim 1 wherein the modifying stepcomprises the step of forming a succession of elevations and depressionsin said surface layer upon said substrate.
 3. The method of claim 2wherein the modifying step comprises the step of forming angled peaksand valleys in the surface of said layer for increasing the barrierproperties of said structure.
 4. The method of claim 1, wherein saidsurface layer comprises a metallic coating.
 5. A method of enhancing theelectromagnetic barrier properties of a substrate which comprises thesteps of(a) applying a surface coating to said substrate; and (b)modifying the surface of said coating by providing a plurality of setsof microembossed patterns on said coating, said plurality of sets ofmicroembossed patterns having a line density between 100 and 50,000lines per square centimeter and having a depth less than the thicknessof said surface layer such that said substrate is not altered, in orderto increase the degree of reflectance of incident electromagnetic energyof falling upon said coating to thereby reduce the penetration of saidsubstrate by the incident electromagnetic energy, said coating beingmetallized.
 6. The method of claim 5, wherein said electromagneticenergy is in the range of visible light.
 7. The method of claim 5,wherein said incident electromagnetic energy has a frequency belowinfrared.
 8. The method of claim 5, wherein said incident energy has afrequency in the range of ultraviolet and beyond.
 9. The method of claim5, wherein said coating comprises a metallic coating.
 10. The method ofclaim 5, wherein said plurality of sets of microembossed patterns areprovided in at least two different degrees of variation.
 11. The methodof claim 10, wherein said plurality of sets of microembossed patternsare in the form of surface corrugations which are disposed at an anglewith respect to each other.
 12. The method of claim 11, wherein theplurality of sets of microembossed patterns form at least a right anglebetween them.
 13. The method of claim 12, wherein the plurality of setsof microembossed patterns are provided by at least three differentembossment patterns.
 14. The method of claim 13, wherein the pluralityof sets of microembossed patterns are uniformly distributed to form asymmetric repetitive pattern on the surface of said substrate.
 15. Themethod of claim 1, wherein each of said plurality of sets ofmicroembossed patterns are in the form of non-parallel surfacecorrugations.
 16. The method of claim 1, wherein said plurality of setsof microembossed patterns are in the form of irregularly spaced surfacecorrugations.
 17. The method of claim 5, wherein each of said pluralityof sets of microembossed patterns are in the form of non-parallelsurface corrugations.
 18. The method of claim 5, wherein said pluralityof sets of microembossed patterns are in the form of .irregularly spacedsurface corrugations.
 19. The method of claim 4, wherein said metalliccoating has a thickness of about 400 Å.
 20. The method of claim 9,wherein said metallic coating has a thickness of about 400 Å.